Melanoma cell growth inhibition by βγ-CAT, which is a novel non-lens betagamma-crystallin and trefoil factor complex from frog Bombina maxima skin

In vertebrates, non-lens βγ-crystallins are widely expressed in various tissues but their functions are unknown. The molecular mechanisms of trefoil factors, initiators of mucosal healing and being greatly involved in tumorigenesis, have remained elusive. βγ-CAT, which is responsible for the potent hemolytic activity and lethal toxicity on mice of frog Bombina maxima skin secretions, is the first example of a non-lens βγ-crystallin and trefoil factor complex. Its α- and β-subunits show significant sequence homology to human Absent In Melanoma 1 and trefoil factors, respectively. Here, we showed that βγ-CAT triggered two types of cellular responses in human melanoma cells. On one hand, the protein (25–200 pM) was able to stimulate cell migration in melanoma A375 cells. On the other hand, it inhibited cell proliferation by delaying S-G2/M cell phase transition. Blockade of the cell cycle was associated with increased p21/WAF1 expression, and reduced amounts of Cdc2 and Cdc25C. βγ-CAT also reduced Cdc2 function by increasing the level of inactivated phospho-Cdc2. In addition, the expression of JunB, a well-known cell proliferation inhibitor, was significantly up-regulated. These results provide the first evidence of an anti-proliferative role for a non-lens βγ-crystallin member and action mechanism via association with a trefoil factor.